In software defined infrastructures, vendors such as cloud service providers, generally host users' applications and handle tasks including system maintenance, backup and resiliency planning. These platforms offer highly scalable resources that can be adjusted on-demand and are well-suited for workloads that are temporary or subject to change.
Cloud computing services are generally provided along the scale of Software as a Service (SaaS), platform as a Service (PaaS), and Infrastructure as a Service (IaaS). These software defined computing environments provide different levels of vendor support to user installations. IaaS provides virtualized computing resources over the Internet in which a third-party provider hosts hardware, software, servers, storage and other infrastructure components on behalf of its users; PaaS adds the operating system (OS), middleware, and runtime components to the vendor provided components; while SaaS adds applications and data to the vendor provided components, so that the user provides only customization parameters.
The allocation of resources in software defined infrastructures, such as the IaaS offerings by cloud providers, is a fundamental challenge. A common example is the automatic creation and destruction of virtual servers in response to changes in service request rates. In most circumstances, automatic scaling employs basic thresholding techniques so that resources are only allocated when a simple trigger condition is reached. For example, increasing the number of servers when overall system load reaches 80% for more than 30 seconds, or decreasing when the overall system load reaches 40% for more than 5 minutes. The thresholds are often defined empirically and fail to take into account models of IaaS (or PaaS) costs associated with server allocations.
To address the shortcomings of current approaches, what is needed are new methods based on reliability theory and that incorporate costs associated with provisioning software defined resources.
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